Communication system



Jan. 18, 1944. J. BAUMFALK 2,339,669

COMMUNICATION SYSTEM '.5 'Y' l I Arron/vtr Jan. 1s, 1944. J. .BAUMFALK A 2,339,669

COMMNICATION SYSTEM Filed Aug. 4, 1942 5 sheets-sheet 2 TO NORMAL WITCH/NG 6 EQUIPMENT DIFFERENT/4L /NVENTOR J BAUMFALK Arron/ver Jan- 18; 1944. .1. BAUMFALK 2,339,669

Y COMMUNICATION SYSTEM y Fiied Aug. 4, 1942 5 sheets-sheet s F/G. la

/N VE N TOR J BAUMML" Jan. 18, 1944. .1. BAUMFALK 2'339',669

COMMUNICATION SYSTEM Filed Aug. 4. 1942 5 sheets-snaai 4.

//VENTOR J BAUMFALK A TTRNE V Jan. 18, 1944. .1. BAUMFALK 2,339,669

` COMMUNICATION ySYSTEM med Aug. 4, 1942 s sham-sheet s ne. /2y

NVENTOR J. BAUMMLK Patented Jan. i8, 1944 COMMUNICATION SYSTEM John Baumfalk, Clifton, N. J., assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York application August 4, 1942, serial No. 453,522

c claims. (o1. 179-27) This invention relates to communication systems and particularly to special service telephone systems.

The object of the invention is to'provide means to establish emergency connections from certain preferred lines in a group served by machine switching means regardless of the busy conditions of the trunks leading from such group of lines and in some cases regardless of the busy conditions of the lines themselves.

For certain emergencyconditions it is necessary that connections be established from certain given lines without delay. Where such lines are in what is known as a community dial exchange it may be found that, when an emergency arises and a particular line is urgently required for immediate service, the line itself is in use or that all trunks outgoing from the exchange are busy. 1t is the object of the present invention to provide means for establishing a connection to a distant point irrespective of such otherwise adverse conditions.

This invention provides means supplementary to the means disclosed in my copending application Serial No. 453,521, filed Aug. 4, 1942, where a communication system in which an operator may establish a connection to a wanted station regardless of the busy condition of the station or the paths leading thereto is disclosed.

In general, when emergency outgoing service is required, the subscriber at a preferred station performs an additional operation which results in transferring his line to a special service equipment. This responds by selecting a trunkto a distant point and if all trunks are found busy then it selects a particular trunk designated for this service and summarily dismisses anyy other connection thereto so as to give mergency service to this preferred subscribers line. y

In accordance with the preferred embodiment of the invention the preferred subscribers station is provided with an emergency switch, generally in the form of a push-button, which upon operation, regardless of the busy or idle condition of the station will immediately transfer the line to a special equipment. The normal connection between the line and the regular switching facilities is summarily broken and a clear path to a distant point is established.

In accrdance with another form of the invention where the arrangement of the circuits is such that the emergency switch cannot paused, the usual subscribers dial is operated to send a predetermined signal by means ofwhich same result may be accomplished.

the

A feature of the invention is a means under control of a calling subscriber to seize a trunk, summarily dismiss any other connection thereto and gain a clear communication channel to a distant point.

Other features will appear hereinafter.

The drawings consist of five sheets having twelve figures as follows:

Figs. 1 to 5, inclusive, are block diagrams showing how the remaining Figs. 6 to 12 may be combined to illustrate various alternative arrangements of the present invention. For purposes off clarity .the circuit diagrams of Figs. 6 to 12 will be described first.

Fig. 6 is a circuit diagram of a substation circuit equipped with a special key at the sub.- station for routing a call outgoing therefrom in either a normal or an alternative direction. Fig. '7 is a similar circuit diagram showing how the selection of a normal or alternative outgoing path may be controlled by an ordinary substation dial. Fig.. 8 is a circuit diagram of an operators two-way trunk circuit which may be employed to extend calls from the regular switching equipment of an exchange over a normal path toward a distant manual ollice. Fig. 9 is an applique -circuit which may be introduced between the outgoing end of the two-way trunk of Fig. 8 and the line Wires extending to the distant manual oiiice. This applique circuit is for converting the trunk to right-of-way service so that the trunk may be seized and used on an emergency call regardless of its busy condition in normal service. Fig. 10 is a circuit diagram showing a simple trunk termination at a distant manual oiiice. Fig. 11 is a circuit diagram showing a trunk termination by which a call extended thereto may be distributed to any one of a number of other terminations. Fig. 12 is a one-way outgoing trunk circuit by means of which the calls may be extended from an exchange to a distant manual ofce.

Figs. 1 to 5, inclusive, are applique diagrams indicating the various combinations of the figures above described to produce various alternative forms of the present invention.

By combining the gures designated as shown in Fig, l a communication system may be illustrated in which an emergency connection may be extended from a given special substation to a distant manual oce. Either of the substation Y circuits of Fig. 6 or '1 may be used in regular service to extend a connection through the normal switching equipment of the exchange and is through a two-Way operators trunk circuit as shown in Fig. 8 to the distant manual oice shown in Fig. 10. It will be understood that the showing of Fig. l is practically schematic in nature since it shows an ordinary line and cut-ofi" relay arrangement and does not illustrate the more complicated circuits which are in use and which perform a number of additional functions. Since it is only necessary here to indicate that the connection isactually extended beyond the ltwo-way trunk of Fig. 8 the simple circuit diagram of Fig. 10 will be suiicient for this purpose.

If an emergency call is to be extended from one of the substations equipped for thisspecial service and all of the trunks to the central oiiice are found to be busy then the special operation to be described hereinafter in'connection'withFigs. 6 and '7 will be performed whereby the connection through the normal switching .equipment y will be cut off and the busy trunk shown in Fig. 1 as e: tending from Fig. 8 through Fig. l9 toFig. i0 will be approached throughthe :blockcircuit 'of- Fig. 9. rltegarolless of the busy conditiontof this trunkfthe connection will be extendeddirectly from Fig. 6 or Fig. v'Tthrough Fig. 9 to rFig, 10 so that access to the distant manualaoicewill be gained immediately.

Fig. 2 shows an alternative arrangement of the invention in which thegreater.scope"is.=given.to

`the calling subscriber. In this case-also thecalling subscriber maygo throughthe normalswitching equipment, that is, through a two-way operators trunkto ardistant exchange. If, however, no availablepaths are -found then through the special operation consistingbfthe operation of an emergency button at thesubstation shown in' Fig. 6 or an operation of the'dial at the substation `as shown `in Fig. 7, a distributing switch ,shown in Fig. ll'will .beseized'which will thereupon hunt for anidle'outgoing .trunk to the distantmanual exchange. In this arrangement all -Aoflthe outgoingitrunks reached bythe distributingswitch of "Fig, 11,'.with the exception of. the

Vlast one will ibe` arranged ordinarily. The last -tiunk, however, willibe a right-of-way trunkfso l that connection will now be 'establishedfrom .the

substation :through the .distributing l switch to the applique circuit of f'Fig. 9`1Wherer a busytrunkis seized'iandappropriated' Vfor emergency use `and thence to thezdistant manualexchange. It will be understood thatall the. trunks reached by. the distributing lswitch` of L'Fig. 11 vdo i not necessarily Y extend to the samedi'stantlmanuall exchange -but Abefore described. V-This is illustratedrby the blocks in Fig. Bshowing thefpossibility of establishing'a connection from --the substation circuits through switch has access lonlyto outgoing-trunks andit will, thereforeycontinue to hunt until `an Vidle `trunk is `encountered even though the brushes of the switch may vhave to` rotate .through -several complete" movements.

Fig. 4-showsfa simple )arrangement in which the r-ight-of-way connection is established directl ly to a manual oiceterm-inationinstead. oigoing i. through a trunk provided -for-normaluse.

65 ling -ofl relay l 6.

particular outgoing trunk of the kind shown in Fig. 12 is set aside for emergency use exclusively according to the arrangement of Fig. 5, a call may be extended from either of the substations 5 of Fig. 6 or Fig. 7 through the normal switching equipment over a two-way trunk to a distant manual office or through the special operation for right-of-way calls may be extended over a one-way trunk to a distant manual oice.

The manner in which these various connections are established in detail will be understood from the following detail description of Figs. 6 to 12,

inclusive.

Fig. 10 is a circuit showing a subscribers line .equipped with' a non-locking key for grounding 'the` line to Vvinitiate an emergency call. The subscribers 'line is connected to a circuit designedforuse as an auxiliary line circuit where it is desired to provide priority service to emergn gency'calls outgoing from the subscribers stavtion. Whenthe receiver is .removed from 1 the -switchhook'at station 'i a circuit is established from battery, upper winding of line relay 2,

`upper .winding of differential relay3, lower left- 25 -hand windingofrepeating coil 4, back contact 'and armature 2 ofrelay 5 over theline circuit tofstation l back 'to Varmature IV and back'con- Ltact of relay 5, .upper left-hand windingof repeating coil lig-lower windingof .differential relay 3, lower .winding2of line` relay 2 to ground. Relay 3does`not'ioperate in this circuit since its windings are :connected ldifferentially but. line relay .2 I responds. Relay "2 establishes a circuit fromltheitipconductor 1 leading tozthe normal --switchngaequipmentover-the back contact and --armaturelZ of relay 6,.upper right-hand winding 'lof repeatingzcoil :4, f resistance 18, `lower right- -hand 'winding fof repeating coil 1.4, armature 5 ;andback'.lcontact'of relay 6, contact and arma- 40 lture-.oflvline relay 2,'armature-3 and back contact iofzrelay Bto the ring conductor 9 leading to the normal switching equipment. Thus, -a

'.bridge/isplaced across conductors -1 and 9 to cause lthe inormal operation -in the switching 5Lequipment beyond. If dialing lis required to `establish a connection, dial pulses are repeated byline'relayZ when the'receiver is placedA on Vthe switchhook. Relay 2 releases, restoringthe circuit` to normal.

IOnia 'normal incoming call to station I ringfing l current passes through condenser It and lvrelayill to operate relay 5 which thereuponfcon- 'nects the conductors 'I and 9 to the front con- -vtacts and armatures l and 2, respectively of 'relayv5- so that the ringing current will reach the substation i. When the subscriber answers -theline relay '2 yw'ill'operate as hereinbefore "described The subscriber lmay originate an emergency -50 call atl any time the receiver is off thehook by operating momentarily Vthe'emergencykey l2. `This'grounds theV line unbalancing thewindings "of relay-"f3 which thereuponv operates 'and' closes ground through thethermistor i3 to the wind- Thethermistori3 is provided #to slowdown the operation of relay-6- so'that it willfnot operate and lock falsely due tomornen ftary'operations of relay 3 on searches. "When thermistor I3 slips sufcien'tlyto V'lower-its re- "sponse to -the proper value, relay 6 operates.

l' Relay l161 operated i (l) disconnects the bridge through resistance-wand repeating coil 4 from Vthe vsubscribers line circuit used v:for-normal foperatio'n, opening any y connectionestablished Fig..5;showslarsimplearrangementlinlwhchf:w75 thereby; (2) -connectsl-this bridge andi-talking path to the manual subscriber line or outgoing trunk for emergency operation connected to conductors I4 and I5 causing the origination of a call thereon; (3) closes an immediate short circuit around thermistor I3 to start cooling it down and to make the slow release feature of relay 6 effective; (4) closes a locking path to the contacts of relay 2 which may or may not remain operated with the emergency key operated, and bridges resistance I6 and condenser Il'I across the subscribers line circuit leading to the normal switching equipment to provide a termination for the continuity test of the terminating marker in the crossbar oices so as to avoid false trouble indications on terminating calls to this circuit while an emergency call is in progress. When the emergency key I2 is released at the station the differential relay 3 releases and the line relay 2 reoperates if it has released. Relay 5 is made slow to release so that it will hold after relay 3 releases until its locking path is closed by the line relay 2. The switchboard termination of the connected line or trunk circuit for emergency operation will be called with suitable auxiliary signals to attract the immediate attention of the operator. The emergency key connection at the station is such that the answer of the operator may be heard even with the key operated.

When the receiver is replaced on the switchhook at the calling station the line relay 2 releases releasing relay 6 and restoring the circuit to normal. No busy condition is placed on the subscribers line circuit for normal operation while this circuit is in use on an emergency call and hence terminating calls under vthis condition will encounter a rather dont answer condition.

Relay 5 is made slow to operate so that it will not be operated by momentary operations of relay II during dialing or flashing. Resistance 8 is required to prevent premature tripping on false operations of relay 2 to the line discharge. Transmitter battery is supplied through the windings of line relay 2 and the usual current limitingresistance (not shown).

Fig. 11 shows a circuit similar in function to that of Fig. except that the emergency connection may be established through the operation of the ordinary subscribers dial rather than through the use of special emergency key; When the subscriber at station I6 removes his receiver from the hook relay I'I operates in turn operating the rst slow relay I8. The circuit for relay I'l may be traced from ground, the upper Winding of relay II, back contact and armature I of ringing relay I9, upper left-hand winding of repeating coil over the line circuit to station I6 through the lower left-hand winding of repeating coil 20, armature 2 and back contact of ringingy of relay 42li, the upper right-hand winding of re-4 peating coil 20, resistance 23, back contact and armature of relay 24,v armature and back contact of relay 25, front contact and armature I of relay I8, lower right-hand winding of repeating coil- 20, armature 2 and back contact of relay f following added functions.

26 to ringing conductor 21. Relay I8 also removes ground normally connected over its armature 3 and back contact to the armature oi.v relay 28.

of the off-normal contacts 30, resistance 3 I, front contact and armature 3 of relay I 8. Relay 29 follows-the code selector indicated by Wiper 32 through its armature I and front contact, relay 29 holds the pulsing relay I8. Relay 29 also provides a pulsing path for the rotary magnet 33 under` control of relay 34. When the calling subscriber dials relay I'I follows the dial pulses removing ground from relay I8 and operating relay 34 on each pulse of each digit. During the dialing of the first digit relay 29 holds relay I8 buty during subsequent digits relay I8 will hold from the front contact of relay 34 and the back contact of relay 29. Upon the first release of the line relay A a circuit is established from ground armature 3 and back contact of relay I9, back contact and armature 2 of relay 2 I, armature and left-hand contact of relay II, armature 2 and front contact of relay I8, armature and back contact of relay 35, winding of relay 34 to battery. Relay 34 operated locks over its front contact and armature 2 under control of relay 35 and closes the supervisory bridge in parallel with the armature and back contact of relay 34. Relay 34 also closes a parallel path for holding relay I8 operated and operates relays 35 and 24. Relay 35 operated opens the locking circuit 4 and releases relay 34 which thereupon releases slowly due to the shunting eilect of resistance 35. Relay 35 prepares a locking circuit for itself in series with relay 25 under control of the left-hand contact of relay I'I. Relay 34 released, opens the pulsing loop, releases relay 24 and allows relay 25 to operate in series with relay 35 opening the pulsing loop at a second point to insure a prompt disconnect at the end of the call.' Relay 24 released,

closes the pulsing loop.

When the line relay I1 reoperates at the end of the pulse relays 35 and 25 release and prepare the circuit for the operation of relay 34 on the next pulse. Relays 34 and 24 are slow in releasing and normally relay 24 is not fully released until relays 35 and 25 have released at the end of the pulse. On fast pulsing relay 24 does not release. Therefore, the release of relay 34 controls the length of closure of the repeated pulse. At low dial speeds relay 24 releases, reclosing the pulsing loop and thereby controlling the open period ofthe pulse and disconnect relays 35 and 25 remain locked up to the back contact and to the left-hand contact of line relay I'I after relay 24 releases. This insures the opening of the supervisory path to the central oil'ice in a minimum time after the pulsing loop is opened thus insuring a'fast disconnect.

In order to get an emergency connection to an operators oiiice certain digits are reserved for each oiiice to which a connection is desired. When the subscriber seizes this circuit relays I1 4and I8 operate as described for a regular call.

The circuit functions as on regular call with the Relay I8 operated, operates relay 29 which holds the relay I8 and -provides a pulsing path for the rotary magnet 33 lunder control of relay 34. When the pulse Vgrounderffunctions relay 34 lfollows pulsation.

from armature ."3 and .front .contact of -relay.; f8 over armature '3"and .back contactfof relay l29 ,to yWiper 32. If the 'digit dialed' was Aone 'assigned for emergency service to fa particular ofcelthen relay `31 associated with thatterminal'willoperate. Relay 31 .operatedoperatesLrelaylZa With relays 26 'and 31 operated the subscriber is i dis- -connected from his Tline .circuit in the .normal switching equipment andconnected through'conductors 38zand 39 for emergency. service 'oven-Circuits tobe 'describedhereinafter.

.Disconnection Vtakes place `in the usual Wav. `When-relay 'I8 releases relays 26 .and .31 release andthe .codeswitch restores to`normal.

.Fig."12 is av circuit diagram ofa two-Way'f trunk circuit with repeating 'coilftransmission-to a man- 'ual ortoll oice. :It isarranged for'tandem'connections overpother orvsimilar two-:Way 'trunk circuits to 'amanual orftoll Ao'irice land to=give a -class of service toner-signalzto.` the rcall operator.

When this :trunk is :seizedfover itstippingfand vsleeve conductors '40, '4I '.and1'42, Vthe relay 43 Voperates and causesfthe operation ofthe 'rs't-fslow 1 relay 44 and relay-'45. Relay A14-operated grounds the sleeve conductor-421501` busy the trunk to other calls. Relay 45 operated reverses battery and `ground-from relay 46 .toward the trunkto operate a polarized-relay ,at 'the distant end as a calling signal. Further description of the operation on a call towardfthe central oliice over this trunk will not `loe given as'it forms no particular part rof the present invention.

Onincoming'calls When the operator seizes this trunkover rconductors '41 and 48, relay 46 operates. ARelay '46 closes thepulsing circuit,plaees a resistance shunt f49about the winding of relay i50 and operatesrelay 5l. Relay 5l grounds the .sleeve over a circuit which may be traced from ground, armature and Jfront co-ntactofrelay 46, armature 2 and back Contact of relay 44, armature I-and back'contact of relay 45,front contactv and armature of relay 5l, armature 6v and front contact of vrelay 5I tothe sleeve conductor 42. The operation ofrelay 5l also transfers the .inside terminals VVofthe repeating 4co-il 52 `fromthe windings of relay 43 vto the Winding 'of yrelay 50 and transfers'theoutside terminals of the re- .peatingcoil to -the'tip. and ring of the incoming .digit .Relay 56 opens the ringlead tetherepeating coil-and .closesftheloop towardthe'incoming .selector through the resistance 51.

.It .should be `Anoted that at `the-righthandrend .ofthe circuit diagram the tip and ring conductors 41 and 48, respectively, are'associated zwithja sleeve conductor 58. In .the case Whererthe'two- Way trunk is used for ordinary service onlyzp-the .tip and vringconductors Will be extended .to ia distant,.oflice. l :In case, howevenfthis; trunk;,s;.to

lchange. of `ligllhave been numbered 41, 1B-.andvv 58, re-

69. .the distant ofi-ice by reversing battery and ground distant cnice as Aa disconnect signal.

v'On :the '.first :pulse :the A.rotary .magnet operates 'stepping the 'code lselector one Aterminal and-:op- .erating the offenormal 'springs\36. :During .subsequent pulsesy re1ay29y holds-operated" in'parallel with the. rotary magnet. When'fthe'nrst :digit Iis i' completed .relay 29 releases connecting-.ground ibe' i used for rightfof "way Aservice then 'the circuit jdiagram'- offFig. -"13 f is inse'rted between this vtrunk and vthe conductors "leading to the distant-ex- Thus, the fthree left-hand conductors spectively to indicate Lthat they` areaused for ex- .tending the two-Waytrunk of Eig. 12.

yThe circuitdiagramfof Fig. 13 is for useasan auxiliary trunk circuit to giveright of Wayvto certain stations.' on emergency .'calls to thev oper- :.ator. oice. When ithisrcircu'it isseized by a subscribersoverthe con`ductorsf59 and 60'Which'may .correspondito'the.conductors I'4-and l5, respectively of Fig. 10 or conductorsf38 vand 39, respec- :tivelyof Fig. 11, relay 6l is operated. :Relay6l operated, .causes the zoperationof relays v62 and .53 .and this latterrelay through'its armature 2 andifront contactand over theback contactand armature of 'relay .645grounds the'sleeve Vconduc- Ator 58;to'actas abusy condition-in the normal .switching equipment. `Relay63 operated'provides :aiholdingground for otherrelays in the circuit and operates the'transfer relay 65 pwhereby the talking circuit toward the central oice is disconnected vfrom'the tip and Aring .conductors41 andt andtransferred to the conductors 59 and Relay-'62 operated sends a seizuresignal to over the tip` and ring. Relay 66 which supplies battery vand ground to the trunk conductors 61 .and` 68- responds to theanswer'of the operator at the distant end. .Assuming that this trunk'was seized over'the conductors 59 jand 60 during its use in some other connection than upon the-operation of relay 65,-relay 66 Will immediately respond since theoperator at the distant office is f-already in on the connection. Relay 66 operated,

operates relay 61. Relay 61 in turn locks .tothe first slow relay 63 and -sends audible ringing to theoriginating subscriber andcauses relay 68 to .operate intermittently in accordance with the interrupter 69. Relayv68 alternately reverses battery and ground to the distant oice to ash the disconnectsignalv in the .distant oice as an emergency disconnect', signal. When the operator thereat disconnects, relay 66 releases, operating .relay-.1,0 .which Vlocks to Nrelay 63..and opens-the flashing .lead restoringrelay 68 to normal. The answeringlamp will light :steadily until .the 0perator Willianswer r.the .call whereupon relay66 again operates Voperatingrelay'H at .this.time.

. Relay 1 l f operated removes audible. ringing, holds relay .B3-operated andoperates relay 12. Relay `12 operated, closes the transmission circuit and locksV to relay 63.

This connection is under-.the control at both ends. Whentheoriginating ends disconnect relay.6l releases, releasing relay V62. 'Relay v62 released reverses battery .and `ground toward the When the distant ofce disconnects relay 66 releases in turn releasing relay 1I. Relay 1| released, re-

lleases relay 63 which in ,turn releases .relays 61, `1.0,12:and565. v.Relay 63 alsoremovesground fromthesleevelead restoring. the circuit to nor- 4mal.

Fig. .14 is alicircui't arrangement Vshowing a .line termination atadistant 'central oflice. This is. a .conventionallcircut -having a line and cutoffrelay and an answering lamp and Will do -in the present instance Vasan indication of some .means .by which the attention of the 'distant oper- :ator may beattracted. `Under normal conditions the.ground.and battery frornsthe line relay 413 will z5 tberpnosed .rtoslike iennectiensfin the .ttunkfso 2,339,669 that the relay 13 will not be operated. Howeven when the trunk is seized as described in connection with Figs. 12 and 13 the ground and battery from the trunk is reversed and this will cause the operation of line relay 13 which will result in the operation of the line lamp 14. When the operator answers the cut-off, relay 15 will respond and open the circuit to the windings of line relay 13 in the usual manner. It will be understood that more complicated trunk circuit terminations may be used at the central oice end in order to perform additional functions but this circuit will suice for the present purposes.

Fig. 15 is a circuit for use in establishing connections from subscribers to an operator oflice and is used as will be more fully explained hereinafter to insure that a subscriber making an emergency call will properly reachv an available trunk to the central oice. The tip and ring conductors 16 and 11 may be variously matched to the tip and ring conductors I4 and |5 of Fig. 10 or conductors 38 and 39 of Fig. 11. When the circuit is seized a loop is closed across the tip and ring leads operating the line relay 10. Relay 18 operated opens the circuit to brush 19 of the selector and closes a circuit to the stepping magnet 80 through brush 8| and armature 2 and back' contact of the cut-oi relay 82. This operates the stepping magnet which steps the brushes to the first terminal in the multiple bank. The connection from the normal terminal of brush 19 to the Winding of the stepping magnet is provided to prevent the switch from stepping over the rst terminal even if it is idle due to the adjustment of the line relay being such that it operates slowly. If the first terminals are busy the sleeve terminal is grounded and this operates the stepping magnet which breaks its own circuit and continues stepping until the idle sleeve terminal is found. When the idle sleeve terminal is found relay 82 operates from ground at the make contact of the line relay 18 to battery in series with the stepping magnet 80. The stepping magnet does not operate in series with the cut-off relay 82. The operation of relay 82 closes the originating loop through wipers 83 and 84 to the circuits selected. The circuit selected operates and in turn holds ground over the sleeve lead and brush 8|. The operation of relay 82 allows relay 18 to release. Relay 18 is designed to release slowly in order to hold ground on the sleeve until the holding ground is returned over the sleeve lead.

When the holding ground is removed 'rom the sleeve lead relay 82 releases. This opens the connections to brushes 8|, 83 and 89 and grounds the bank terminals for brush 19 which operates the stepping magnet and returns the switch to its normal position.

Fig. 1'7 is a circuit diagram of a trunk circuit outgoing from -a step-by-step office to a distant A switchboard or manual office. When this circuit is seized over its tip, ring and sleeve conductors 85, 86 and 81, the line relay 88 will be operated and this in turn will operate the auxiliary line relay 89 which will ground the sleeve 81. Relay 89 also energizes the sleeve relay 90 and the holding relay 9| and short-circuits the upper windings of relays 92 and 93. Relay 89 also removes condenser 94 from its normal connection across the tip and ring leads 85 and 86 and closes the talking circuit through the back contacts of relay 95. The sleeve relay 90 grounds the sleeve when operated and is slow to release to maintain the ground potential on the sleeve during momentary releases of the line relays 89 and 89. Relay-'9| operated, operates relay 96 which grounds the sleeve and operates relay 95 to the back contacts of relay 91. Relay 95 closes the audible ringing tone circuitand throws battery and ground through the windings of relay 91 and to the trunk. Relay 91 does not operate at this time but the battery and ground through its windings causes the trunk lamps at the incoming ends to be lighted.

When the operator answers a high resistance bridge at the distant end is removed and batteryv is placed onthe ringing conductor and ground on the tip conductor- This battery and ground aid the battery and ground of relay 91 and relay 91,

therefore, operates. Relay 91 locks `to ground from the relay 96 and at the same time opens the circuit of relay 95. Relay 95 releases and removes the audible ringing tone to the calling subscriber and at the same time opens the windings of the' relay' 91 toward the distant en d. Relay l 95' through its back 'contacts connects a dry 'bridge on the trunk. Thus atthe present time a circuit may be traced from conductor 98 through' the upperl right-hand winding of repeating coil 99, armature I and backcontact of relay 95, lower l winding of relay 93, lower winding of relay 92,

talking bridge.

armaturev I 'and front contact of relay 89, back contact and armature 2 of relay`95, lower right-` hand winding of repeating coil 99 to conductor |00. Relay 92operates from the battery and ground at the distant ,end and-holds relay 9| operated. Relay 9| is slow to release so as to remain operated from the time its energizing path was opened by the operation of relay 91 until -it is again energized by the operation of relay 92.

This trunk circuit is provided with a ring back feature whereby the calling subscriber or seized trunk may be called. When the distant operator throws her ring back key, ringing current is transmitted over the ring conductor of the interofce trunk. Relay |0| respondsand causes the operationof relay |02 which inturn `causes the operation of relay |03. Relay |03 connects ringing current from the contacts of relay I 04 to the tip and ring conductors and 86.

Should the subscriber disconnect first relay 88 releases and opens the operating path for relay 89. Relay 89 releases and in turn removes the short circuit from around the upper high resistance windings of relays 92 and 93 giving the operator a disconnect signal and opening the The sleeve relay 90 releases after the relay 89 has restored to normal. Relays 92 and 93 release if operated when the operator disconnects. The release of relay 93 releases the reversing relay |05 and the release of relay 92 releases relay 9| and in turn relay 96. Relay 96 removes ground from the sleeve and releases relay 91.

Should the operator disconnect first, relays 92 and 93 release. The release of relay 92 releases relays 9| and 96. This causes relay 91 to release which completes the path for reoperating relay 9| from the contacts of relay 89. Relay 9| then reoperates relay 96 which energizes relay 95 throwing battery and grounds to the windings 81 on the trunk which relights the trunk lamp. Should the operator answer before the calling ends has disconnected the circuit functions as hereinbefore described. When the calling end disconnects before the operator answers relays.

What` is claimed is;

1. lIna:communication system; agroup of lines,1.

machine switching; means` forv interconnecting said-lines, trunks leading fromsaidgroupto a distant point; special service meansfor giving a-preferredonef-offsaid lines'a clear channel over oneofsaid `trunks comprising means under control -ofl the subscriber on said preferredone of said linesifor summarily disconnecting said line from its normal connectionr to saidmachinec switching means and connecting said lineto'an idle; one of saidtrunks;

2. Inza communication system,v argroup of lines;

machine switching; means for` interconnecting. said lines, trunksileadingirom saidgroup to af distant point, special service means for givingal preferred oneofr said lines `a clear channel over ai: predetermined one of said trunks. comprising means.-.under control .ofi the subscriber. on saidpreferredfone'of saidrlines for seizing said predetermined trunks and summarilydismissingany existing -norma-l': connection. thereto.-

3: In a communication system; a group of lines; machine.- switch-ing;` means; forv interconnecting said lines,Y trunksfleading;from1said group Vto a distant point,Y speciall service means: for giving a prefer-red: one off said: lines: a clear; channel .over one-of saidtrunks. comprisingmeanssunder conf trol of; the subscriberon said.. preferred; one oi?4 said lines for: summarilyfdisconnecting the said line fromitsfnormal;connectionto'- said machine switchingmeans;for connecting fthe said line tov therstidle oneiof saidtrunks, andmeansresponsive to. the busyY condition. of. all. of; said trunksl for?` seizing a predetermined. onev of said trunks and summarily dismissing` anyl normal connection thereto:

4.'.In a communication .system,. agroupof lines,

machine switching means; for1 interconnecting. said11ines, trunks leading from. said group to. a.V

distantipoi'ntan auxiliary line circuit Yfor a pre'- ferred"- oneci'said lines comprisinga transfer relaygga normalconnection through the contacts of said'relay, between said line. and said .machine switching. means;` throughthe. operated contactsv of said relaybe gezogene preferred'one .of said lines comprising a transfer relay,.anormalvconnection through the contacts of said relay between said line and saidmachine= switching means, an alternate connection throughthe operated'contacts of said'relayfbetween saidlline and a special service 1ine,.saidv special-,serviceflineand means controlled thereover toestablish a. clear communicationchannel over. one `of said trunks to said distant'point,` and a special services switch. under control ofv the subscriberrat .the substation on saidpreferred one of said-,lines-for controlling said auxiliar-y line circuit.-

6.A 1n a communication system, a group l.of lines, machine switching` meansV for interconnecting. said.lines,trunks leadingirom said:group toa distant point, anfauxiliaryline circuit for apre ferredcneof said lines comprisingv a transfer relay, a normalconnection throughthe contacts of .said relay between-saidline and said'machine an alternate connection1 tween said line and a special serviceeline', saidf specialserviceline and means controlled thereovertovestablish a clear communication channel Aover' one `of said .trunks to :said distant point,` said-` auxiliary-line circuit being under control ofthe substation .dial-at ,the substation on the said preferred one lof 'saidflines JOHN B-AUMFALK. 

